This invention relates generally to a fuser release agent management system for an electrophotographic printing machine, and more particularly to apparatus for controlling the dispensing of release agent material in accordance a calculated print equivalency value for prints fused which corresponds very closely to the amount of release agent consumed.
In a typical electrophotographic printing process, a photoconductive member is charged to a substantially uniform potential so as to sensitize the surface thereof. The charged portion of the photoconductive member is exposed to selectively dissipate the charges thereon in the irradiated areas. This records an electrostatic latent image on the photoconductive member. After the electrostatic latent image is recorded on the photoconductive member, the latent image is developed by bringing a developer material into contact therewith. Generally, the developer material comprises toner particles adhering triboelectrically to carrier granules. The toner particles are attracted from the carrier granules to the latent image forming a toner powder image on the photoconductive member. The toner powder image is then transferred from the photoconductive member to a copy sheet. The toner particles are heated to permanently affix the powder image to the copy sheet.
In order to fix or fuse the toner material onto a support member permanently by heat, it is necessary to elevate the temperature of the toner material to a point at which constituents of the toner material coalesce and become tacky. This action causes the toner to flow to some extent onto the fibers or pores of the support members or otherwise upon the surfaces thereof. Thereafter, as the toner material cools, solidification of the toner material occurs causing the toner material to be bonded firmly to the support member.
One approach to thermal fusing of toner material images onto the supporting substrate has been to pass the substrate with the unfused toner images thereon between a pair of opposed roller members at least one of which is internally heated. During operation of a fusing system of this type, the support member to which the toner images are electrostatically adhered is moved through the nip formed between the rolls with the toner image contacting the heated fuser roll to thereby effect heating of the toner images within the nip. Typical of such fusing devices are two roll systems wherein the fusing roll is coated with an adhesive material, such as a silicone rubber or other low surface energy elastomer or, for example, tetrafluoroethylene resin sold by E. I. DuPont De Nemours under the trademark Teflon. In these fusing systems, however, since the toner image is tackified by heat, it frequently happens that a part of the image carried on the supporting substrate will be retained by the heated fuser roller and not penetrate into the substrate surface. The tackified toner may stick to the surface of the fuser roll and offset to a subsequent sheet of support substrate or offset to the pressure roll when there is no sheet passing through a fuser nip resulting in contamination of the pressure roll with subsequent offset of toner from the pressure roll to the image substrate.
To obviate the foregoing toner offset problem, it has been common practice to utilize toner release agents such as silicone oil, in particular, polydimethyl silicone oil, which is applied to the fuser roll surface to a thickness of the order of about 1 micron to act as a toner release material. These materials possess a relatively low surface energy and have been found to be materials that are suitable for use in the heated fuser roll environment. In practice, a thin layer of silicone oil is applied to the surface of the heated roll to form an interface between the roll surface and the toner image carried on the support material. Thus, a low surface energy, easily parted layer is presented to the toners that pass through the fuser nip and thereby prevents toner from adhering to the fuser roll surface. Apparatus for applying the release agent material to a fuser member is commonly referred to as a release agent management system.
Release agent management systems designed for copier environments having relatively low average monthly print volumes (AMPV) and lower stress documents are not suitable for high volume printers, particularly those capable of creating color or highlight color images. With the high AMPV expected from high speed printers and the high stress matrices expected from tri-level xerography the exposure to offsetting (from low oil)is a large concern. Simply increasing the oil addition rate would cause problems with excess oil on first output prints and would stress the oil removal system increasing the oil on print defect exhibited in the past by high volume printers.
As will be appreciated, it is desirable to provide a RAM system which can provide varying oiling rates in accordance the number of prints created.
The following publications may be relevant to various aspects of the present invention:
U.S. Pat. No. 5,099,289 discloses a fuser silicone oil dispenser which utilizes a metering member and a donor member and which is capable at operating in two modes to vary the amount of silicone oil delivered to the fuser.
U.S. Pat. No. 4,942,433 describes a release liquid applying device utilizing a rotating wick that is engaged by a fusing roller wherein the wick at times is prevented from rotating, thereby reducing the oil applied to the fuser roller.
U.S. Pat. No. 4,593,992 describes a device for intermittently applying the fuser release agent to the rotating fuser roll.
JP-A-164,085 describes a fuser assembly in which a solenoid actuated lever increases or decreases the amount of release agent applied to the fuser assembly by the donor member.
JP-A-476,672 describes a fuser member in which another solenoid actuated lever arm rotates to disconnect the donor member from the fuser oil supply to thereby reduce the amount of oil applied to the heated fuser member.
JP-A-107,979 describes a fuser assembly in which an adjusting blade is regulated as to its contact with a donor member to vary the amount of release oil applied to the heated fuser member.
JP-A-35,569 describes a heated fuser assembly in which the speed of the donor member is regulated to control the amount of oil supplied to the heated fuser roll.
U.S. Pat. No. 4,920,382 granted to Mills et al on Apr. 24, 1990 discloses a roller fixing device, for example, a pressure roller fuser includes a roller to which a release agent is to be applied by a wick. To correct a tendency of certain wicks to apply the release liquid in a pattern including spots of locally excessive liquid, the wick is disengaged from the roller sufficiently prior to the fixing operation to permit the liquid to spread eliminating the spots of locally excessive liquid. Preferably, the roller completes at least one revolution in contact with another roller after disengagement and prior to the beginning of fixing. To assist that spread, a sheet of more absorbent material, for example paper, is fed through the fixing operation during this period. This mode of operation is used for specific receiver sheets and toner conditions, for example, those encountered in making color transparencies. A more conventional wicking mode is used for other reproductions on paper and black toner transparencies.
U.S. Pat. No. 5,132,739 granted to Mauer et al relates the curing of background defects by adjusting the oiling algorithm used in applying offset preventing liquid in the fuser. According to a preferred embodiment, no oil or less oil is applied when fusing the first image to the receiving sheet when the apparatus is operating in the duplex mode. When operating in the simplex mode or fusing the second image to a sheet, a normal amount of liquid is applied.
U.S. Pat. No. 4,549,803 to Ohno et al, issued Oct. 29, 1985 and U.S. Pat. No. 4,593,922 to Yoshinaga et al, issued Jun. 10, 1986, both show fixing devices in which fixing conditions are changed between paper stock and transparency stock to reduce the amount of oil applied when transparencies are being fixed.
U.S. Pat. No. 4,429,990, issued Feb. 7, 1984 to E. J. Tamary discloses an applicator for applying release liquid to a fusing roller which contacts the toner image. The applicator, commonly called a rotating wick, includes a hollow, porous roller which is supplied with fusing oil internally. The applicator has an inner supply tube with holes in it and is covered by a porous material having a surface of wool or a heat resistant synthetic wicking material. The applicator is rotatable by the fusing roller. The applicator is movable into and out of engagement with the roller according to a program which prevents excess buildup of oil on the roller, which otherwise would stain the receiving sheet.
U.S. Pat. No. 5,214,481 granted to Linn C. Hoover on May 25, 1993 relates to an oil application system which is controlled by actuation and deactuation of a wick actuation solenoid in the receiving apparatus. The solenoid depresses a wick plunger to rotate the wick into rolling engagement with a fusing roller, i.e., the wick is moved clockwise around a wick pivot point, into a first position. The wick is spring urged to a second position separated from roller when the solenoid is not actuated and the plunger is not depressed. Movement of the right end of actuator arm downward causes the left end to pivot upward. A pin is coupled between the left end of an arm and cradle to move the cradle clockwise around a pivot. A typical wicking algorithm would call for deactivation of the solenoid after a certain number of copies to prevent over-oiling of the fusing roller. The algorithm may vary according to the type of receiving sheet and the type of image. Such algorithms are well known in the art and are implemented by a logic and control. It is known that the greater force applied between the wick and the fusing roller, the greater the oiling. Thus, an alternative construction would move the wick between positions in which more and less oil is applied. In the embodiment shown, the wick is either applying oil or not.
U.S. Pat. No. 5,212,527 granted to From et al on May 18, 1993 describes a release agent management system including a metering roll and a donor roll in which a metering blade structure for metering silicone oil onto the metering roll has two modes of operation. In one mode, a wiping action of the metering blade meters a relatively large quantity of silicone oil to the roll surface and in the other mode of operation, a doctoring action is affected for metering a relatively small amount of silicone oil to the roll surface.
U.S. Pat. No. 5,227,270 granted on Jul. 13, 1993 to Scheuer et al discloses a single pass tri-level imaging apparatus wherein a pair of Electrostatic Voltmeters (ESV) are utilized to monitor various control patch voltages to allow for feedback control of Infra-Red Densitometer (IRD) readings.
The ESV readings are used to adjust the IRD readings of each toner patch. For the black toner patch, readings of an ESV positioned between two developer housing structures are used to monitor the patch voltage. If the voltage is above target (high development field) the IRD reading is increased by an amount proportional to the voltage error. For the color toner patch, readings using an ESV positioned upstream of the developer housing structures and the dark decay projection to the color housing are used to make a similar correction to the color toner patch IRD readings (but opposite in sign because, for color, a lower voltage results in a higher development field).
U.S. Pat. No. 5,202,734 granted to Pawlik et al on Apr. 13, 1993 discloses A release agent management system including a metering roll supported for contact with release agent material contained in a sump. A donor roll is provided for applying oil deposited thereon by the metering roll. Prior to fusing taking place, the donor roll is supported in pressure engagement with the fuser roll and out of contact with the metering roll. During fusing the donor roll is cammed into engagement with the metering roll.
U.S. Pat. No. 4,496,234 granted to Joseph G. Schram on Jan. 29, 1985 discloses a release agent system for use with a heat and pressure fuser. The system is characterized by the use of a reciprocating, positive displacement pump for delivering silicone oil the heated fuser roll. The pump is actuated in response to the fuser rolls being engaged and disengaged, such movement being adapted to act against one or the other of a pair of springs which in cooperation with the oil being pumped forms a damper system which is utilized to control the quantity of oil delivered. The springs and oil cause the velocity of the pump's piston to decay with time which results in more oil being pumped initially.
U.S. Pat. No. 4,079,229 granted to Koichi Takiguchi on Mar. 14, 1978 discloses a contacting and heating fixing apparatus comprising a first roll of which the surface has a coating of a heat-resistant material with which a toner image of a material to be fixed comes into contact, a second roll for pressing, heating and fixing the material to be fixed in cooperation with said first roll, and a supply mechanism for supplying an offset inhibitor liquid to said heat-resistant parting material on the surface of said first roll, characterized in that supplying of the offset inhibitor liquid from said supply mechanism is made only at warm-up time of a copier.
U.S. Pat. No. 4,593,992 granted to Takada et al on Jun. 10, 1986 discloses an image forming apparatus for forming an unfixed image on a recording material includes a fixing device having a pair of rotatable members for holding therebetween and conveying the recording material to fix the unfixed image on the recording material, speed control device for variably controlling the fixing rotational speed of the pair of rotatable members to a first fixing speed and a second fixing speed lower than the first fixing speed, application apparatus for intermittently supplying a parting agent to at least one of the pair of rotatable members, and application control apparatus for variably controlling the application acting period of the application apparatus in accordance with the fixing rotational speed of the pair of rotatable members variably set by the speed control device.
U.S. Pat. No. 4,429,990 granted to Ernest J. Tamary on Feb. 7, 1984 discloses apparatus for controlling the application of fuser release material such as fuser oil to a roller fuser in an electrographic copier. The number of fixable images or the number of photoconductor frames are counted after the start of a copy run and compared with the number of copies which exit from the copier to determine if the two counts bear a preselected numerical relationship to each other. If they do, fuser oil is applied to the roller fuser; if they do not, application of fuser oil is discontinued until the two counts bear such numerical relationship.
U.S. Pat. No. 4,272,666 granted to Vittorio Coilin on Jun. 9, 1981 discloses a fusing rolls fixing unit having a toner antisticky liquid supply device wetting the surface of the fixing rolls to prevent adhesion of toner particles thereto. The antisticky liquid supply device is discontinuously operated for applying liquid to the fixing rolls only one time for each copy-run executed.